Kinetic Molecular Theory

Question 1

Assumptions

Answer 1

Gas consists of molecules of mass m.
Gas has random motion.
Straight line movement between collisions.
Size of molecules is negligible
Molecules not interacting which undergo perfectly elastic collisions

Question 2

Evidence of molecular motion

Answer 2

Flow: Gases flow to fill a volume

Question 3

Evidence of molecular motion (Thermal Expansion)

Answer 3

When a gas is heated, particles will move faster and push outwards more

Question 4

Evidence of molecular motion (Brownian Motion)

Answer 4

This is when small particles move randomly due to many collisions

Question 5

Evidence of molecular motion (Diffusion)

Answer 5

This is the transport of matter through a gas, we see this when gases mix

Question 6

Origin of pressure

Answer 6

Molecular collisions with wall of container create pressure. The collisions experience a change in momentum, this change in momentum is the pressure.

Momentum = mass*velocity

Question 7

Kinetic energy of a single molecule (equation)

Answer 7

E(KE) = 1/2 (ms^2)

Question 8

Mean Kinetic energy per molecule (equation)

Answer 8

Line(E(KE)) = 1/2 (mc^2), this equation is derived from:

pV = 1/3nNa(mc^2)

Question 9

Combining kinetic theory and ideal gas

Answer 9

pV = 1/3nNa(mc^2) & pV = nRT.

c^2 = 3RT/Mr, where Mr is the molar mass.

c = root(3RT/Mr)

Question 10

Graham’s law of effusion

Answer 10

At a given temperature and pressure the rate of effusion is inversely proportional to the square root of the molar mass.

Rate of effusion = 1/root(Mr)

Small Mr = More effusion

Question 11

Mixing of two gases (equation)

Answer 11

Rate of effusion A/Rate of effusion of B which is the same as equation:

Mixing of two gases = (Ma/Mb)^1/2, where Ma, Mb are molar masses wrt. their reactants A and B

Question 12

Define Effusion

Answer 12

Effusion is when a gas is escaping through a hole

Question 13

Define Diffusion

Answer 13

This is when different gases are mixing

Question 14

Collision cross-section (equation)

Answer 14

(pi)diameter^2 = pi(2radius)^2 = sigma

Question 15

Collision frequency (equation)

Answer 15

z = root(2)Na(c(sigma))(p/RT)

Question 16

Mean free path (equation) and exception

Answer 16

lambda = RT/ [root(2)NaSigma*p],

Please note that this equation is for systems where molecules are considered as hard spheres. (Ideal Gases)

Question 17

Phase transition diagram

Answer 17

Phase transition is when the graph(line) is horizontal left to right at a given pressure.

Question 18

Define a Real Gas

Answer 18

Real gases cannot be an ideal gas, these gases DO have attractions between molecules

Question 19

Van der Waals equation (Real Gases)

Answer 19

(p+a(n/V)^2)(V-n*b) = nRT

where, a accounts for intermolecular interactions and b accounts for the finite size of molecules

Question 20

Temperature (a & b)

Answer 20

T(subscript c) = 8a/27Rb

Question 21

Pressure (a & b)

Answer 21

P(subscript c) = a/27b^2

Question 22

Volume (a & b)

Answer 22

V(subscript c) = 3b

Question 23

What is a and b?

Answer 23

a: Attractive interactions
b: Real volume of molecules in a gas

Question 24

Interactions present in a real gases & sticky collisions

Answer 24

Hydrogen Bonding
London Dispersion
Dipole-Dipole Interactions
Dipole Induced (This causes sticky collisions)